DCAT-mapping of CKAN “extra” keys

The CKAN software allows portal providers to include additional metadata fields in the metadata schema. When retrieving the metadata description of a dataset via the API, these keys are included in the resulting JSON under the key “extras”. However, it is not guaranteed that the DCAT conversion of the CKAN metadata contains these extra keys. Depending on the version and configuration of the DCAT export-extension there are three different cases:

1) Portal-specific mapping

The portal provider defines a mapping for certain CKAN fields to a specific RDF property.

2) No mapping

Looking at the same dataset, we can see that there are other “extra” keys where no mapping to an RDF property exists, e.g., for the key collection-name. The metadata information will get lost if we only consider the exported DCAT.

3) Generic mapping by extension

Certain CKAN data portals map all available extra metadata keys by using the dct:relation (Dublin Core vocabulary) property. The key gets mapped to the rdfs:label property and the value to the rdf:value property, e.g., for the contact-email metadata key: